This invention relates to core bars for a rubber track, and more particularly to a rubber track traveling device mainly for use in construction equipment, earthworking equipment and the like.
Although rubber tracks have been used mainly for agricultural equipment, recently they have been employed for construction equipment and earthworking equipment. The rubber track includes an endless belt-shaped rubber-like elastic member, a number of core bars embedded therein and aligned in the longitudinal direction thereof and extending in traverse directions thereof, and steel cords (tension-resistant members) embedded in the endless elastic member to surround the core bars circumferentially outwardly. As such, rubber tracks are made of rubber-like materials, vibrations to be transmitted to occupants are mitigated and paved roads are not damaged. Therefore, rubber tracks have been used willingly.
On the other hand, however, when a vehicle equipped with rubber tracks moves on sandy terrain or quarries, the rubber tracks are likely to shift from advancing directions of the vehicle due to elongations and contractions of the rubber-like material in vertical and horizontal or other directions. As a result, the rubber tracks unavoidably get off sprocket wheels or track rollers of the vehicle. Various attempts have been made in order to prevent the dislodgement of the rubber tracks from the vehicle, but they have not met with success.
The present invention relates to an improvement of an inner track roller type rubber track whose core bars are formed with driving protrusions on the inner circumference of the rubber track. FIG. 1 illustrates in cross-section a prior art rubber track of the inner track roller type and FIG. 2 is a longitudinal sectional view of the rubber track. The core bar 2 of the rubber track includes wings 3 and 4 on both sides embedded in the rubber-like elastic member 1, a bridging center 5 connecting the wings 3 and 4, and a pair of protrusions 6 and 7 provided on both sides of the bridging center 5 and projecting from the inner circumferential surface of the rubber track. The core bars 2 are surrounded outwardly by steel cords 8 embedded in the rubber-like elastic member 1 in its longitudinal directions. As can be seen from the drawings, the bridging center 5 of the core bar 2 engages teeth of a sprocket wheel 9, and the elastic member 1 between the bridging centers of core bars 2 is formed with recesses 10 for the sprocket wheel 9. A track roller 17 provided on a vehicle rolls on the passage between the protrusions 6 and 7.
The bridging center 5 of the core bar 2 is required to have a predetermined width and a predetermined thickness for engagement with the sprocket wheel 9. Therefore, when the track roller 17 rolls between the protrusions 6 and 7 of the core bars 2, it repeatedly rides over the bridging centers 5 and falls onto the recesses 10 of the elastic member 1. As a result, personnel on the vehicle unfavorably undergo violent vibrations or oscillations. This is the largest disadvantage of the inner track roller type rubber track although it has a certain effect for prevention of rollers getting off the track. Such a disadvantage is unavoidable so long as the bridging center 5 engages the teeth of the sprocket wheel 9.
On the other hand, there is another driving system in which a rubber track is directly formed in its circumference with driving protrusions adapted to engage driving wheels. In this system, there is a tendency for small stones to jam between the driving protrusions and the driving wheels which cause cracks in the inner circumferential surface of the rubber track. Particularly, when track rollers roll on the inner circumference of the rubber track, sand and small stones tend to jam between track rollers and the rubber track to cause cracks in the inner circumferential surface of the rubber track. Therefore, this driving system involves a problem in durability for use as a rubber track.
FIG. 3 illustrates another prior art rubber track, which is used for construction equipment and can be usually used in place of an iron shoe crawler. Core bars 2 made by casting or forging are embedded with constant intervals in an endless rubber member 1. The core bar 2 includes wings 3 and 4, an engaging portion 5 engaging sprocket wheels, and protrusions 6 and 7 on both sides of the engaging portion 5 and projecting onto the inner circumference of the rubber track. Track rollers 9' roll on the upper surfaces of the protrusions 6 and 7. In the case of the iron shoe crawler, the track rollers 9' roll on links (not shown). Moreover, steel cords 8 as tension-resistant members are embedded usually in a row in the endless rubber member 1 on the outer circumferential side of the wings 3 and 4 of the core bars 2.
In rubber tracks used in large type construction equipment, the width of the tracks is often several tens cm, and core bars 2 used in the rubber tracks are much longer and thicker, whose weight is as much as several kg. Therefore, the weight of a rubber track including a number of such heavy core bars 2 embedded therein is as much as several hundreds kg. However, only the engaging portions of the core bars engaging the sprocket wheels serve to receive the driving force for driving the heavy and bulky rubber track.
On the other hand, the rubber track 1 is always subjected to tensile forces when it is running. Only the core bars 2 serve to maintain the rubber track 1 in a flat state against such tensile forces. Therefore, the center portions of the core bars 2 are subjected to great moments of inertia. Moreover, as the rubber track is formed along its longitudinal center line with recesses in a row for the sprocket wheels so that the longitudinal center portion of the rubber track is devoid of steel cords. As a result, the steel cords are divided at the center portion into two groups. Therefore, the wings 3 and 4 become longer and thus moments acting upon the core bars become larger as well. In conjunction with these facts, the center portions or the sprocket wheel engaging portions 5 of the core bars 2 must be wider and thicker in addition to the longer wings 3 and 4. As a result, great amounts of the material are needed for the rubber tracks.
In the prior art rubber track shown in FIG. 3, moreover, the two protrusions 6 and 7 of the core bar 2 are needed for traveling surfaces for the track roller 9'. Although these two protrusions 6 and 7 serve to prevent the rubber track from getting off, they are wasteful for the material of the core bar. What is worse still, when running on rocks or inclined surfaces, inclinations of the track roller 9' and the rubber track 1 become different so that the rubber track 1, particularly the protrusions 6 and 7 are likely to move away from the track roller 9' so that the rubber track unavoidably gets off from the vehicle.